problem burning hole in piston

[matthew1]

what could it be? just rebuilt this engine everything is new in it. one cyl. keeps burning hole inpiston after ten minutes of riding.set carbs by specs. is it sucking air from crank seals or could it be the carbs?

[beerdart]

It could be either. Did you rebuild the carbs? Did you rebuild the bottom end or just install a piston? How about some history on the ski. Make model. Has it ever run good how long have you owned it etc:

[matthew1]

had the ski two years ran great till this year. its a sl 750. rubuilt the engine from crank up. even rebuilt the carbs. how can i put pressure in the engine to check for leaks around the crank seals

[beerdart]

Block off the Intake manifold and exhaust apply 9-10 psi thru the pulse fitting and it should hold for 5-8 min.

[Polaris_Nut#1]

Which piston? It could be you missed the boat. Everybody is doing a fuel pump upgrade on these.

[beerdart]

Also crank index is it a rebuild crank?

[matthew1]

i put a new upgrade fuel pump behind the other fuel pump and also has new crank.and it is the last cyl. that keeps burning a hole in it.

[ph2ocraft]

matt, Go back and do it ALL.
All new hoses, don't forget the ones in the tank (if applicable)
New fuel valve
New Fuel Pump (stand alone), I prefer the triple outlet or high volume as that of a 96 SLX780.
Clean the carbs, filters especially.
Like beer stated check the crank index and of course check for air leaks.